The present invention relates to a transparent radiation shielding structure which may be used for, for example, a work face of a glove box that is designed to handle radioactive substances safely.
We will hereinafter discuss a work face of a glove box for handling radioactive substances in nuclear facilities as a prior art that is related to the present invention. However, it should be noted that the application of the present invention is not necessarily limited thereto and that the invention maybe generally applied to radiation shielding structures that are required to be transparent.
Referring to FIG. 2, a conventional glove box 21 has a work face 22, which is formed with glove ports 23 having gloves (not shown) attached thereto and passing therethrough, and a worker, using the gloves, handles a radioactive substance in the box.
The work face 22 of the glove box 21 must be capable of shielding radiation and also transparent so that the worker can view the inside of the box 21. In addition, the work face 22 must have a satisfactorily airtight structure.
The conventional work face 22 has a double-panel structure comprising an airtight panel 24 made of a transparent acrylate resin material and a radiation shielding panel 25 of a transparent lead acrylic resin material (or lead glass) that is disposed outside the airtight panel 24, as shown in FIG. 3.
The airtight panel 24 is brought into contact with a panel mounting portion 27 through a gasket 26 for airtight seal that is fitted to the outer peripheral edge of the panel 24. In addition, a retaining plate 29 is pierced with a plurality of bolts 28 that are provided on the panel mounting portion 27, and the airtight panel 24 is fastened with a nut 30 through the retaining plate 29, thereby securing the airtight panel 24 to the panel mounting portion 27.
The transparent radiation shielding panel 25 is disposed outside the airtight panel 24 to shield radioactive rays, e.g., neutron beams, gamma rays, etc., by lead that is contained in the radiation shielding panel 25.
The reason why the prior art adopts the double-panel structure comprising the airtight panel 24 and the radiation shielding panel 25 is that, if the radiation shielding panel 25 is attached directly to the panel mounting portion 27 through the gasket 26, which is fitted to the outer peripheral edge of the panel 25, to form a single-panel structure, lead that is contained in the radiation shielding panel 25 is oxidized by chemicals, e.g., nitric acid, in the box 21 to form an oxide film on the panel surface, resulting in the panel 25 becoming opaque, so that it becomes difficult to view the inside of the box 21.
The above-described prior art suffers, however, from the problems stated below.
Since a gap 31 is present between the airtight panel 24 and the radiation shielding panel 25, which constitute a double-panel structure, the opposing surfaces 24a and 25a of the two panels 24 and 25 become cloudy with moisture or are stained with suspended dust, resulting in a lowering in the transparency. In addition, radiation cannot be shielded at the edge of the gap 31 between the airtight panel 24 and the radiation shielding panel 25, so that radioactive rays leak therethrough. Further, since two panels 24 and 25 need to be mounted, the assembly operation efficiency is low.